I recently replaced my Defender's turbo. Since then it's had an issue.
When it gets hot the speedo goes mad when I accelerate, jumping about or dropping to zero.
When it does this the boost also drops off, then back on, then off, etc.

On advice I replaced the vehicle speed sensor, but either the new one doesn't work or I've done something catastrophic, because the speedo doesn't work at all - so no boost - until the engine gets hot and then the speedo and boost become juddery as before.

There is probably a problem with the new sensor (or it's not fitted right), but as the original fault is still there, could the turbo be at fault? I've checked the wiring connection and it looks fine.

A replacement speed sensor arrived but before I fitted it I thought I'd try the original back in.
This now also gives the same result - i.e. no speedo reading at all.
I checked the connector and wiring, dirty but otherwise looks fine.
Cleaned it and put it back - same issue.
Any suggestions gratefully received!

Ok so it seems the sensor positioning is critical; the plunger needs to sit in the dip of the bit inside the transfer box or it won't work.
Not easy to tell when fitting as you can't see very well, but a mirror gave me a clue.
Sorted! Now just need to work on the boost issue when hot!

bukko said:

Ok so it seems the sensor positioning is critical; the plunger needs to sit in the dip of the bit inside the transfer box or it won't work.
Not easy to tell when fitting as you can't see very well, but a mirror gave me a clue.
Sorted! Now just need to work on the boost issue when hot!

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Did you have any luck with this? I also have a 2.4 Puma that suffers loss of power and speedo in hot weather with the air on switched on! The previous owner had replaced the turbo, so I wonder if it’s the same issue..

Dommo_b said:

Did you have any luck with this? I also have a 2.4 Puma that suffers loss of power and speedo in hot weather with the air on switched on! The previous owner had replaced the turbo, so I wonder if it’s the same issue..

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Yes, weirdly it turned out to be EGR valve. Loads of problems went away after I - erm - fixed that.